Split ring seal

ABSTRACT

A split ring face seal made from self lubricating graphite material. The seal has applications to in board boat drive lines. The split ring seal allows for a method to effectively manufacture and ultimately to re-manufacture the face seal. The seal includes centering bearing surfaces that allow for some elastic flexing in response to torsional stress within the drive line while limiting drive shaft wear caused by such flexing in the drive line. The split ring face seal is designed to be driven against a stationary seal face. The face seal is adaptable to virtually all types of boat drives as well as providing a practical seal in other applications.

BACKGROUND OF THE INVENTION

[0001] In the inboard motor boating industry there is a need to seal thepropeller drive shaft where it passes through the hull of the boat. Inthe field of large vessels it had been common practice to employ a“stuffing box” to seal the propeller drive shaft. These packing sealswere prone to leak and a constant source of maintenance problems for theboat operators.

[0002] The stuffing box seal caused environmental concerns in boatingapplications. The inherent friction between the drive shaft and thepacking material required a constant low volume flow of lubricating oilto the seal. Even when properly maintained oil would seep through theseal and contaminate the water.

[0003] Recent advances in composite materials have made it possible todo away with the stuffing box. The water seal is now being maintained bya precisely machined and polished composite material face driven againsta stationary split ring face seal on the stern tube.

SUMMARY OF THE INVENTION

[0004] The present invention relates to advances in composite materialseal facings that allow for more efficient system that is easier tomaintain. The seal is a split ring which is necessary for large vesseldrive lines typically those with a drive shaft diameter over 3 inches.The present device allows the seal to be serviced as necessary withoutremoval of the entire propeller shaft drive assembly.

[0005] A drive line having a split ring face seal including a split ringface seal of self lubricating material is formed from two half ringsjoined at two polished surfaces. A seal face on said split ring faceseal, and the split ring face seal having an inside diameter and anoutside diameter with a rotatable drive shaft passing through the insidediameter of the seal face. The split ring face seal includes a pluralityof raised fiber bearing surfaces integrally formed on the insidediameter of the split ring face seal such that relative movement betweenthe split ring face seal and the drive shaft can cause the raised fiberbearing surfaces to contact the outside diameter of said drive shaft tokeep the split ring face seal centered.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006]FIG. 1 Shows a view of the seal

[0007]FIG. 2 Shows an edge view of the seal

[0008]FIG. 3 Shows a cross sectional view of the seal installed in aboat drive line

[0009]FIG. 4 Shows a cross sectional view of details of manufacturingthe seal face

[0010]FIG. 5 Shows an exterior view of the drive line

[0011]FIG. 6 Shows a prior art seal and;

[0012]FIG. 7 Shows a cross section of the prior art seal assembly

DETAILED DESCRIPTION OF THE DEVICE

[0013]FIG. 1 shows a face on view of the back surface split ring faceseal (10). The split ring face seal (10) is made in two separate halvesjoined at polished facings (12). The face seal (10) includes a pluralityof raised bearing surfaces (14) on the inside diameter (22) of the seal(10), machined simultaneously as the face seal (10) is being created.The plurality of raised bearing surfaces (14) form a gapped inner mostdiameter (24) (shown as a dashed line) that allows for water to flowaround the outside diameter of drive shaft (101 in FIG. 3). The faceseal (10) includes a plurality of threaded bolt holes (18) and at leastone drive pin hole (20). The material used for the face seal (10) can beany dense, stable, self-lubricating composite such as agraphite-impregnated fiber. One such material goes by the commercialname of Simsite. FIG. 2 shows a cross sectional edge on view of the faceseal (10). The cross section shows surface (30) and seal face (32).Shoulder diameter (34) provides a location for a compression band (shownin FIG. 3, 124), preferably of nitrile, that holds the split ring faceseal (10) together during assembly of the split ring face seal (10).Shoulder (39) provides a surface for the thrust boot (110 shown in FIG.3) to seat on and groove (38) can aid in maintaining a clean facesurface on seal face (32). The groove (38) helps wash away sediment thatmay get on face (108) before it can become trapped between faces (108)and (32).

[0014]FIG. 3 shows a cross sectional view of the face seal (10) and boatdrive line (100). The drive shaft (101) drives a propeller (102) outsidethe stern tube (104) of the boat. The stern tube (104) includes a matingring (106) that is typically a coated carbide, stainless steel orsimilar corrosion and wear resistant material. The mating ring (106) canbe pinned to the stern tube (104) and held to the stern tube (104) bycompression from the thrust boot (110). The fixed face (108) of the ring(106) contacts the moving face (32) (shown in FIG. 2) of the split ringseal (10). The interface of fixed face (108) and moving face (32) formthe water tight mechanical seal between the rotating drive shaft (101)and the fixed boat stern tube (104). The drive shaft arrangementincludes a solid rubber thrust boot (110). This rubber thrust boot (110)is clamped to the drive shaft (101) by a split ring steel clamp (120)and turns with it when the drive shaft (101) is rotating. Duringinstallation of the split ring face seal (10), the thrust boot (110) isaxially compressed and then held by the clamp (120) and secured by bolts(122, FIG. 5) so that the thrust boot (110) holds the face seal (10) andring (106) in compression against each other and against the stern tube(104). The thrust boot (110) includes an integrally molded brass ring(112) that stiffens the boot (110) and carries a drive pin (114). Thedrive pin (114) drives the face seal (10), which rotates with the driveshaft (101). The seal arrangement includes a nitrile rubber compressionband (124) wrapped around the split ring face seal (10). The nitrilerubber compression band (124) holds the face seal (10) together and inplace during assembly and provides a water tight seal for the brass ring(112) of the boot (110) against the face seal (10). A similararrangement seals the back of the stationary ring (106) to the sterntube (104). FIG. 3 also shows that the sealing arrangement forms ahollow area (300) that in use will be filled with water. There areseveral sealing joints but only the planar surface between face seal(10) and the stern tube ring (106) forms a mechanical self lubricatingseal between two parts moving relative to one another. The fixed face(108) and moving face (32) must match up perfectly to avoid leaks.

[0015]FIG. 4 shows a portion of the manufacturing process for the splitring face seal (10). The face seal (10) starts out as a cylindrical orring shaped fiber material blank (200) shown in phantom lines. The backsurface (30) is machined and polished. The blank (200) can be split andthe facings (12 in FIG. 1) between the two halves are accuratelymachined and polished. Threaded holes (18) are installed in the backsurface (30) of the blank (200) so that the split blank (200) can bemounted on a fixture (310) using bolts (314), stainless steel inserts(not shown) can be used for holes (18). The fixture (310) can then beattached, using bolts (312) to the rotatable master fixture (300) whichcan be mounted in the rotatable chuck of a lathe (316). Once mounted thecritical diameters (14, 16) and moving face (32) of face seal (10) maybe concentrically turned from the blank (200). This process assures theparallelism of thrust shoulder (39) and seal moving face (32). After allturning and facing processes are complete, the critical sealing surfacemoving face (32) is polished while the split ring face seal (10) isturning counter clockwise in the lathe (316). Course abrasive can beused in a first rough polish step. Then the direction of rotation of thelathe (316) can be reversed during course abrasive and then the nextfiner polish grit is applied. The direction of rotation can be reversedwith each finer grit abrasive until the surface is finished. The blank(200) can be rotated clockwise and counterclockwise with each grit. Thisprocess of reversing allows for a much finer finish to be achieved withthe fiber faces then would be possible if the same direction of rotationwere maintained throughout the polishing process. The polishing processremoves all traces of composite fiber base from the seal face (32). Theprocess also enables the thrust shoulder (39) and seal face (32) to bemachined and polished perfectly parallel to each other maintaining aflatness tolerance of plus or minus 0.0001 inches on the seal face (32).This process is far superior to polishing or lapping with aunidirectional method (lathe turning one direction) which allowsremnants of the fiber base to remain on the seal face (32) preventing awater tight seal between the mating faces (32 and 108).

[0016] One advantage of a split ring face seal is that it can be removedfrom around a large drive shaft (101) when it is worn and a replacementface seal (10) installed without going to the time and expense ofpulling the entire drive shaft (101). FIG. 4 also demonstrates theability to reface worn face seals (10). In the case of refacing a seal(10) that is worn, the split ring face seal (10) is re-installed on thefixture (310) after it is removed from a boat, using original bolt holes(18). The face seal (10) is then re-machined and polished to regain the0.0001 inch flatness tolerance and mirror smooth finish required forthis application. This manufacturing process is critical to theapplication allowing for finishes, flatness and parallelism that givethe face seal (10) a much longer life then current seals in the sameapplication. The process also allows re-manufactured seals which savessubstantially over the original cost of the face seal (10) which cancost several thousand dollars each. Typically both the stationary ring(106) and rotating face seal (10) are serial numbered and maintained asa matched pair and can be reconditioned/refaced at the same time.

[0017]FIG. 5 shows an exterior view of the drive line (100) includingthe face seal (10) as it would appear in a boat prior to disassembly.The drive shaft (101) powers the propeller (102) on the exterior of theboat stern tube (104). The stern tube (104). The stern tube (104)provides a mounting surface for the opposing stationary split ring(106), which can be tungsten carbide, with a fixed face surface (108)that acts as half of the sealing structure. The rubber boot (110) isheld in compression by the steel split ring clamp (120) which is bolted(122) in place and turns with the drive shaft (101).

[0018]FIG. 6 shows the prior art seal (510). The prior art seal (510)does not include bolts holes in the original manufacture so it in notpossible to re-surface the sealing face after use. It is not practicalto attempt to install holes (108) in a face seal (510) that did notoriginal have them. The prior art seal (510) used Delrin inserts (514)as bearing elements against the drive shaft (101). It was discoveredthat inserts (514) were undesirable because they wear into the driveshaft (101) over time weakening the shaft (101) and reducing theeffectiveness of the bearing surface (14).

[0019]FIG. 7 gives more detail on the operation of the prior art faceseal (510). The prior art seals require water lubrication. Water fromnear the drive shaft (500) is pumped via pump (550) through line (552)through the stern tube (504) to line (554) that opened into the sealface (508) on tungsten carbide ring (506). A slot opening (560)circulates water around the face of ring (510) to lubricate. The wateris necessary to keep the seal surface cool and because the prior artseal material is not self lubricating. Like the current device thrustboot (530) and clamp (522) maintain the sealing arrangement incompression. This prior art arrangement is undesirable because of theadded expense and maintenance of the pump (550) but also because pumpingwater, even filtered water, will contaminate the polished seal faces andlead to failure of the seal (510).

[0020] Referring again to FIG. 3, in use the face seal (10) wouldtypically be placed in a fairly large vessel such as a tow boat. Thedrive line (100) powers the propeller (102) and the void (300) fillswith water which must be sealed out of the boat. The mechanical sealbetween moving parts occurs between the ring (106) fixed face (108) andthe split ring face seal (10) moving face (32). The rubber boot (110) iscompressed and holds the face seal (10) against the ring (106). Tow boatoperation involves frequent shifts in the application of power throughthe drive line (100), often going from forward to reverse and back inquick succession. Under such loading the rubber boot (110) and driveshaft (101) flexes and can cause the bearing surfaces (14) to come upagainst the drive shaft (101). Prior art seals as shown in FIG. 6 usedDelrin inserts (514) as the wear surface between the face seal (510) andthe drive shaft during these shifts. These Delrin inserts (514) requirea separate manufacturing process and are not diametrically accurate andinteract with the shafting material in a way which damages the shaft.The Delrin inserts (514) have a small surface area and require a specialoperation to drill a hole and insert them into the seal (510). Thecurrent invention replaces these inserts (514) with integrally formedbearing surfaces (14). The bearing surfaces (14) are formed on a rotarytable in a milling machine (not shown) while the face seal (10) is stillattached to the fixture (310) which is attached to a master millingfixture (not shown) similar to the lathe fixture (300). The bearingsurfaces (14) can be as large as required for bearing wear and yet stillprovide for the flow of water around the drive line (100). Part of thefunction of the bearing surfaces (14) is to keep any portion of the sealface (32) from coming off the face (108) and becoming exposed to water.Exposure to dirty water would accelerate the wear of the moving face(32) and fixed face (108). The bearing surfaces (14) keep the face seal(10) centered around the drive shaft (101) during drive line (100)loading that might otherwise cause the face seal (10) to come offcenter.

1. A method of manufacturing a split ring face seal made from fibermaterial including the steps of: forming a blank of fibrous material;splitting the blank along a planar surface to form two halves; polishingthe planar surface on each of said halves; forming threaded holes intothe blank and mounting the blank to a lathe using said threaded holes;turning a seal face onto the blank; polishing the seal face.
 2. Themethod of claim 1 wherein the step of polishing includes rotating theblank in a clockwise and then in a counter clockwise direction whilepolishing the seal face.
 3. The method of claim 1 wherein the step ofpolishing includes rotating the blank in a counter clockwise and then ina clockwise direction while polishing the seal face.
 4. A boat driveline having a split ring face seal including; a split ring face seal ofself lubricating fiber material formed from two half rings joined at apolished surface; a seal face on said split ring face seal said sealface and said split ring face seal having an inside diameter and anoutside diameter; a drive shaft having an outside diameter smaller thanthe inside diameter of the seal face and passing through the insidediameter of the seal face; a plurality of raised fiber bearing surfacesintegrally formed on the inside diameter of the split ring face seal;said plurality of raised fiber bearing surfaces forming a gapped innermost diameter smaller then said inside diameter of said split ring faceseal surface but larger then said outside of said drive shaft such thatrelative movement between said split ring face seal and said drive shaftcan cause at least one of said raised fiber bearing surfaces to contactthe outside diameter of said drive shaft, and wherein said drive shaftpowers a propeller.
 5. The boat drive line of claim 4 wherein a rubberthrust boot surrounds said drive shaft and holds said split ring faceseal in compression against a ring fixed to a stern tube and whereinsaid split ring face seal is rotatable with said drive shaft.
 6. Theboat drive line of claim 5 wherein said thrust boot is pinned to saidsplit ring face seal.
 7. The boat drive line of claim 5 wherein saidsplit ring face seal is formed from a blank of self lubricating fibermaterial and wherein said seal face is formed on said blank by rotatingsaid blank on a lathe in clockwise and then in a counter clockwisedirection while applying polishing grit to said seal face.
 8. A driveline having a split ring face seal including; a split ring face seal ofself lubricating material formed from two half rings joined at atleaston polished surface; a seal face on said split ring face seal, said sealface and said split ring face seal having an inside diameter and anoutside diameter; a rotatable drive shaft having an outside diameter andpassing through the inside diameter of the seal face; a plurality ofraised fiber bearing surfaces integrally formed on the inside diameterof the split ring face seal such that relative movement between saidsplit ring face seal and said drive shaft can cause at least one of saidraised fiber bearing surfaces to contact the outside diameter of saiddrive shaft.
 9. The drive line of claim 8 wherein said split ring faceseal is mounted for rotation with said rotatable drive shaft.
 10. Thedrive line of claim 9 wherein a thrust boot is mounted on said rotatabledrive shaft and holds said split ring face seal in sealing engagementwith a fixed ring.
 11. The drive line of claim 10 wherein said seal faceand a face on said fixed ring form a seal holding fluid in a void aroundsaid drive shaft.
 12. The boat drive line of claim 10 wherein saidthrust boot is pinned to said split ring face seal and is compressedbetween a clamp on said drive shaft and said fixed ring.
 13. The boatdrive line of claim 12 wherein said split ring face seal is machinedfrom a blank and wherein said seal face is formed on said blank byrotating said blank on a lathe in a clockwise and then in a counterclockwise direction while applying polishing grit to said seal face. 14.The drive line of claim 11 wherein said drive shaft passes through astern tube and is connected to a propeller.